Electroconductive Bonding Material and Electric/Electronic Device Using the Same

ABSTRACT

A conductive bonding material having an improved preservation stability, and hardens when desired, preferably immediately hardens at a low temperature is provided. In one invention, the conductive bonding material comprises a conductive particle ingredient, an epoxy resin ingredient, and a hardening agent ingredient for said epoxy resin and the hardening agent ingredient for said epoxy resin further comprise a reforming agent having a thiol group. In another invention, a conductive bonding material comprising an epoxy resin hardening ingredient, wherein said epoxy resin hardening ingredient contains a sulfur-containing compound having an end group which can coordinate with a surface of the metallic particles, and the sulfur-containing compound comes to perform as a hardening agent for the epoxy resin by dissociating from the surface of the metallic particles. The conductive bonding material may contain fragrance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electroconductive (hereinafter, alsoreferred to as “conductive”) bonding material comprising anelectroconductive particles ingredient, an epoxy resin ingredient and anepoxy resin-hardening ingredient, a method for producing anelectric/electronic circuit, as well as an electric/electronic devicehaving such an electric/electronic circuit.

2. Description of Related Art

In the field of producing electric/electronic circuits, anelectroconductive bonding material, i.e. an electroconductive adhesiveis widely used for the purposes of mounting electric/electroniccomponents (hereinafter, also collectively referred to as “electriccomponents”) onto a circuit board and the purposes of forming conductorpattern on a circuit board. The electroconductive adhesives, which areused in the field of mounting the electric components, basically havinga composition comprising a resin composition as a binder and conductiveparticles of such as metallic particles which are dispersed in the resincomposition. The conductive adhesives, wherein the resin composition hasa paste-like form, are referred to as the conductive paste.

Such resin composition contains a resin-hardening ingredient, whichmakes the resin composition harden by being subjected to a condition,e.g. by being subjected to a predetermined temperature condition. When aconductive adhesive is subjected to a predetermined temperaturecondition, the resin composition therein volumetrically shrinks whilehardening, so that the volume of the resin composition as a wholedecreases. As a result, the conductive particles which were dispersed inthe resin composition come to contact one another and form a continuousconductive path through the hardened conductive adhesive.

As an example of such conductive adhesives, there is an epoxy-basedconductive adhesive composition which contains an epoxy resin as theresin composition, a hardening agent for hardening the epoxy resin, andmetallic particles such as silver or nickel as the conductiveingredient. The conductive adhesive compositions of such type hardensgenerally by being heated to a temperature of 120 degree centigrade ormore.

Recently, electric components having lower heat resistance property arefrequently used in connection with the advancement of the functions ofelectric components. Accordingly, a conductive adhesive (i.e. a bondingmaterial for mounting) which hardens at a lower temperature is highlyrequired. Further, considering the operability at work sites,preservation stability for a period from several days to several weeksin the adhesive component state is also required for a one-componentadhesive composition as mentioned in the above.

Intending to prepare a conductive adhesive paste having lower hardeningtemperature, applying one-component type epoxy resin composition havinga low hardening temperature, which has been known as an adhesivematerial, to a conductive paste is examined. For example, a resincomposition containing an epoxy resin, a thiol compound as the hardeningagent and a latent hardening promotor of solid dispersed type is knownas an adhesive (Patent Document 1). Furthermore, aiming to improvepreservation stability, a conductive paste containing a borate estercompound in addition to the above composition is proposed (PatentDocument 2).

[Patent Document 1] Japanese Patent Kokai Publication No. 211969/1994

[Patent Document 2] Japanese Patent Kokai Publication No. 2000-230112

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Based on the technical background as mentioned above, one object of thepresent invention of the present application is to provide a conductiveadhesive for mounting electric components, which can be hardened at arelatively low temperature and has an improved preservation stability.Another objects of the present invention is to provide a method ofpreparing circuit boards using the present conductive adhesive formounting and to provide electric/electronic components being equippedwith such circuit boards.

Another object of the present invention of the present application is toprovide a conductive paste which can be hardened at a desired condition,preferably can be quickly hardened at a relatively low temperature andhas an improved preservation stability without an additional componentsuch as borate ester compound. Another object of the present inventionis to provide a method of producing circuit boards and electriccomponents mounted products (or body) using such a conductive paste.

It is not preferable to use compounds having a thiol group (—SH) as ahardening agent of the epoxy resin in view of health and safety, sincean operator handling the compounds feel uncomfortable with theparticular unpleasant stench which is inherent in the thiol group andwhich is emanated from the compounds at the work site. In addition, itis not easy to visually identify or optically determine the end of thehardening reaction based on the change of color tone since, on the onehand, unhardened epoxy resin is generally transparent and changes itscolor tone when hardened, and on the other hand, the conductive fillers(i.e. conductive particles) contained in the conductive paste aregenerally opaque.

Thus, another object of the present invention is to provide a conductivepaste, which can prevent or reduce emanating unpleasant stench and allowthe operator to identify the end of the hardening reaction more easilyrelating to an epoxy-based conductive adhesive. A further object of thepresent invention is to provide a method of producing circuit boards andelectric components mounted products using such a conductive paste.

Means for Solving the Problems

The present application provides an invention of a conductive bondingmaterial comprising a conductive particle ingredient, an epoxy resiningredient, and an epoxy resin-hardening agent, wherein the epoxyresin-hardening agent further contains linear or cyclicsulfur-containing compound. It is preferable that such sulfur-containingcompound is a compound that has a thiol group (—SH).

According to one aspect, the first invention in the present applicationprovides a bonding material for mounting (or a conductive adhesive)comprising an epoxy resin, a latent hardening promotor for hardening theepoxy resin and conductive particles, wherein the bonding materialfurther contains sulfur-containing compounds at a ratio of about 1 to100 parts by weight on the basis of 100 parts by weight of the epoxyresin.

Since the sulfur-containing compound has a SH-group therein, the “—S—”moiety in the compound inherent in the SH-group attacks the C+(carbocation) in the epoxy group through a nucleophilic substitutionreaction to open the epoxy ring, thereby the hardening reaction starts,according to the bonding material for mounting of the first invention.

Contrary to it, the other reforming agent, for example the reformingagent of a silane-based, a titanate-based and an aluminate-basedcoupling agent (or surface treatment agent) can not start the hardeningreaction. When such coupling agent is added to the conductive adhesivecontaining an epoxy resin and a latent hardening promotor and having astandard hardening condition of about 10 minutes at a temperature of 120degree centigrade, on the one hand, adhesion strength could be somewhatimproved, and on the other hand, hardening property would be rarelyinfluenced, or rather higher hardening temperature would be required,for example a hardening condition of heating at a temperature of 130degree centigrade for about 10 minutes would be required.

According to the bonding material for mounting of the first invention,the epoxy resin-hardening ingredient is activated and the epoxy resiningredient can be hardened by being heated at a relatively lowtemperature, for example at a temperature from about 70 degreecentigrade to 110 degree centigrade for about 10 minutes since thebonding material contains a sulfur-containing compound at an adequateamount. Therefore, when the bonding material for mounting of the presentinvention would be used, electric components can be mounted on a circuitboard with avoiding thermal damage and without the necessity ofparticular treatment and/or apparatus, even when the electric componentshad an allowable temperature limit of 120 degree centigrade or lower.Further, the bonding material for mounting of the present invention hasan advantage that it has an improved preservation stability and it issuitable for producing circuit boards successively (or at the sameconditions).

The amount of the sulfur-containing compound is about 1 to 100 parts byweight based on 100 parts by weight of the epoxy resin. On the one hand,sufficient decreasement of the hardening temperature is not attainedwhen the amount of the reforming agent is less than about 1 part byweight, and on the other hand, sufficient preservation stability is notattained when the amount of the reforming agent is more than about 100parts by weight.

In one embodiment, the bonding material for mounting of the firstinvention further contains a thickening agent. It becomes to be possibleto suitably supply the present bonding material for mounting to desiredregions on the circuit board depending on the methods such as transferprinting, screen printing, dispensing by adjusting the viscosity of thepresent bonding material for mounting by adding a thickening agent.

Another aspect of the present first invention also provides anelectric/electronic device containing one or more circuit boards, whichboards one or more electric components were mounted on using the presentbonding material of the first invention.

Those circuit boards can be prepared by a method comprising the steps:

supplying the bonding material of the first invention to predeterminedregions (typically, electrodes or land areas) on the boards;

arranging electric components on the boards by contacting the electriccomponents (in particular, the electrodes of the electric components)with the bonding material;

heating the bonding material at a temperature of 70 to 110 degreecentigrade to harden the epoxy resin; and thereby the electriccomponents are mechanically and electronically bonded (i.e. mounted) tothe electrodes on the circuit board, wherein the above steps are carriedout in the above sequence.

The present application provides, as a second invention, a conductivebonding material as recited in claim 1 characterized in that theconductive particles ingredient are metallic particles and thesulfur-containing compounds are co-ordinated with the surface of themetallic particles, and that the sulfur-containing compounds(thiol-compounds) remove (or dissociate) from the metallic particles tochange to the epoxy resin-hardening agent by being subjected to apredetermined condition.

The present second invention, in one embodiment, is characterized inthat the conductive particles comprise metallic particles selected fromthe group consisting of gold, silver and copper.

The present second invention, in another embodiment, is characterized inthat subjecting to a predetermined condition is to subject to any ofultraviolet ray irradiation, electron ray irradiation and heatingoperation. According to any of these operation, the epoxyresin-hardening ingredient can be activated.

The present second invention, in another embodiment, is characterized inthat the metallic particles have a mean particle diameter ranging from 1nm to 100 micrometer.

The present second invention, in another embodiment, is characterized inthat the metallic particles have a mean particle diameter ranging from 1nm to 100 nm.

As the conductive paste for circuit preparing application or connectingcircuit layers application, it is known that metallic particles innano-size (i.e. the dimension in the order of nanometer (nm))(hereinafter, also referred to as “metallic nano-particles”) aredispersed in a liquid medium. Since the metallic nano-particles havehigher activity rather than metallic particles having larger diameter ordimension and easily agglomerate together at normal temperature, theyhave a problem relating to the preservation stability. In order todissolve the problem, a method comprising adding dispersing agent to themetallic nano-particles, which dispersing agent can form coordinate bondwith the metallic nano-particles, thereby the metallic nano-particlesbeing protected and stabilized, and then eliminating the dispersingagent from the metallic nano-particles by heating and trapping them byacid-anhydrides (for example, see the Japanese Patent Kokai Publication2002-299833).

The inventors have completed the present invention as a result ofextensive and intensive efforts, while paying attention to the matterthat the coordinating state of the sulfur-containing compounds to themetallic particles can be controlled by use of the sulfur-containingcompounds.

In accordance with the first aspect of the second invention, there isprovided a conductive paste comprising metallic particles, asulfur-containing compound and a resin characterized in that thesulfur-containing compound coordinates at the end group thereof with thesurface of the metallic particles, and then the end group performs asthe hardening agent for the resin component after being dissociated fromthe surface of the metallic particles.

According to the conductive paste as mentioned in the above, thesulfur-containing compound can coordinate at the end group thereof withthe surface of the metallic particles (hereinafter, thosesulfur-containing compound are also referred to as “coordinatablesulfur-containing compound” in the present specification), do notperform as the hardening agent for the resin component in thecoordinating state and performs as the hardening agent for the resincomponent in the state that it dissociated from the surface of themetallic particles. In short, the coordinated sulfur-containing compoundis one kind of latent hardening agent. The hardening reaction of thelatent hardening agent can be inhibited by capping the end group thereofthrough the coordinated bond, which group can cause hardening reaction.When the end group is freed by breaking the bond, the agent can causethe hardening reaction. These conductive paste can show highpreservation stability while the sulfur-containing compound keepscoordinating state, and start hardening reaction by dissociating thecoordinated bond when desired. In particular, when a sulfur-containingcoordinatable compound having a function as a hardening agent at a lowtemperature in a dissociated state is used, the paste can show animproved preservation stability and can immediately harden at a lowtemperature when desired.

In the context of the present invention, the recitation “performs as thehardening agent” means that it causes hardening reaction of the resincomponents, for example, by facilitating the bonding reaction among theresin components or by forming cross-link among the resin componentsthrough bonding with the resin components.

It is necessary for the end group of the coordinatable sulfur-containingcompound that it can form a coordinated state with the metallicparticles in a normal state and break the coordinated state whendesired. Such end group may be those containing one or more ofcoordinated atoms having lone-pair electrons. The coordinated bond amongthe metallic particles and the coordinated atoms can be broken byexternal influences, such as irradiation of ultraviolet ray or electronray or by being heated. The exposure dose of ultraviolet ray or electronray and the temperature and period of heating may be optionallyselected. In addition, it is further necessary that the end group of thecoordinatable sulfur-containing compound contributes to the hardeningreaction of the resin and performs as a hardening agent, while thedegree of such properties may vary depending on the combination of theresin to be used and hardening method. The coordinatablesulfur-containing compound may immediately perform as a hardening agentin its dissociated state, or alternatively, may perform as a hardeningagent by being subjected to any external influences, such as by beingheated.

The end group of the coordinatable sulfur-containing compound may be,for example a thiol group. The thiol group can coordinate with a metaldue to having a sulfur atom having lone-pair electrons and contributesto the hardening of resins, in particular the fast hardening of epoxyresins at a low temperature. The examples of such coordinatablesulfur-containing compounds are, for example, alkane thiol compounds, inparticular monothiol compounds such as 1-decanetihol and 1-hexanethiol,polythiol compounds such as 1,10-decanedithiol, 1,8-octadithiol and1,6-hexanedithiol and the other mono- or poly-thiol compounds which haveone or more thiol end group. In general, the hardening period ofpolythiol compounds is rather shorter than that of monothiol compounds.

As the epoxy resins, un-hardened epoxy resin, that is, a resinousmaterial having two or more epoxy groups in one molecule may be used.For example, epoxy resins which are known in the prior art, such asglycidyl ether type epoxy resins, glycidyl ester type epoxy resins,glycidyl amine type epoxy resins and cyclic aliphatic type epoxy resinsmay be used. Alternatively, precursors of such compounds may also beused.

The present second invention is not limited to the above matters and canuse optionally suitable materials as the coordinatable sulfur-containingcompound and resins without departing from the concept of the invention.For example, the end group of the coordinatable sulfur-containingcompound may be an amino group.

The metallic particles may be those comprising metallic materialsselected from the group of gold, silver and copper. Although it is notintended to limit the present invention, the sulfur atom in the thiolgroup as mentioned in the above can suitably coordinate with the surfaceof the metallic particles comprising such metallic materials, on theother hand, it substantially not coordinate with the surface of themetallic particles comprising for example nickel particles.

In one embodiment of the second invention, the metallic particles have amean diameter for example between about 1 nm and 100 micrometer,preferably between about 1 nm and 100 nm. A conductive paste usingmetallic particles having a mean diameter between about 1 nm and 100micrometer exhibits favorable printing property when applied to printingmethods and attains sufficiently low resistivity as a conductivematerial after the resin hardened. A conductive paste using nano-sizedmetallic particles having a mean diameter between about 1 nm and 100 nmmay cause metallic particles to sinter at a relatively low temperature,so that particularly lower resistivity can be stably achieved relativeto the volumetric change of the hardening resin due to temperaturevariation. When the conductive paste is preserved, metallicnano-particles are protected and stabilized by the presence of thecoordinatable sulfur-containing compound, so that adequatedispersibility and preservation stability can be attained withoutcausing the problem relating to the agglomeration of metallicnano-particles.

In one embodiment of the second invention, the conductive paste cancontain two or more kinds of metallic particles and the coordinatablesulfur-containing compound can coordinate at the end group thereof withthe surface of at least one kind of metallic particles. These metallicparticles may have different mean diameters. For example, it ispreferable that the conductive paste contains the nano-sized metallicparticles and the other metallic particles having larger diameters. Whenthe combination of the metallic particles having different meandiameters is used, the filling density of the metallic particles isimproved, while the printing property is also improved rather than usingmerely nano-sized metallic particles. Further, use of such combinationof the metallic particles can decrease the material cost by decreasingthe relative amount of the expensive nano-sized metallic particles inthe metallic particle ingredient.

In the conductive paste of the present second invention, the ratio ofthe metallic particles, the coordinatable sulfur-containing compound andthe resin can be selected, so that the coordinatable sulfur-containingcompound performs as the hardening agent for the resin and the metallicparticles can contact with each other or get closer to each other toexhibit sufficient conductivity after the resin volumetrically shrinkedand hardened.

The conductive paste of the present second invention may contain theother optional ingredient in addition to the metallic particles, thecoordinatable sulfur-containing compound and the resin, which otheroptional ingredient may be suitably selected depending on theapplications of the conductive paste.

The conductive paste of the present second invention can be preparedthrough any available and suitable methods. In such methods, it ispreferable that the constituent ingredients such as the metallicparticles and the coordinatable sulfur-containing compound (without atleast the resin) are firstly prepared, and thereafter the remainderingredients containing the resin are combined with the above preparedconstituents to obtain the conductive paste so as to prevent thecoordinatable sulfur-containing compound from performing as thehardening agent for the resin (i.e. so as to prevent causing hardeningof the resin) before the coordinatable sulfur-containing compound makecoordinate bonds with the surfaces of the metallic particles. It ispreferable for the metallic particles being used for preparation of theconductive paste that they have sufficient chemical activity so that thecoordinatable sulfur-containing compound can make coordinate bonds withthe surfaces of the metallic particles, i.e. the surface of the metallicparticles are exposed without being coated with for example withoxidized film-layer.

The management and the handling of the conductive paste of the presentsecond invention as mentioned in the above during production are easy,so that the present conductive paste may be used for variousapplications. For example, the present conductive paste may be used asthe material for forming a circuit wiring pattern on a circuit board;for forming conductive connections among a plurality of circuit wiringpatterns on a plurality of circuit boards (including double sidedcircuit boards); and for bonding materials for forming mounted electriccomponents.

In accordance with the second aspect of the present second invention,there is provided a method of preparing a circuit board having acircuit-wiring pattern on the surface of said board comprising:

applying a conductive paste of the present second invention to a circuitboard in a pattern corresponding to the desired circuit wiring pattern;

subjecting the conductive paste to any of ultraviolet ray irradiation,electron ray irradiation and heating operation, thereby dissociating thesulfur-containing compound from the surface of the metallic particles;and

causing the sulfur-containing compound to operate the hardening agent,thereby hardening the resin, wherein the above steps are performed inthe above sequence.

Such a method has an advantage that management and the handling of theconductive paste during production are easy, so that the method can beperformed at a relatively low temperature compared with the method usingconventional conductive pastes. When the conductive paste containing thenano-sized metallic particles is used in the above method, a circuitboard having low and stable wiring resistivity can be provided.

In accordance with the third aspect of the present second invention,there is provided a method of preparing a circuit board having acircuit-wiring pattern on the surface of said board comprising:

subjecting a conductive paste of the present second invention to any ofultraviolet ray irradiation, electron ray irradiation and heatingoperation, thereby dissociating the sulfur-containing compound from thesurface of the metallic particles;

applying the conductive paste to a circuit board in a patterncorresponding to the desired circuit wiring pattern; and

causing the sulfur-containing compound to operate the hardening agent,thereby hardening the resin, wherein the above steps are performed inthe above sequence.

Such a method has an advantage that management and the handling of theconductive paste during production are easy, so that the method can beperformed at a relatively low temperature, preferably with least heatingof the circuit board and the other parts optionally arranged on theboard, compared with the method using conventional conductive pastes.When the conductive paste containing the nano-sized metallic particlesis used in the above method, a circuit board having low and stablewiring resistivity can be provided.

In accordance with the fourth aspect of the present second invention,there is provided a method of preparing a multilayered circuit board,wherein a plurality of wiring layers are superposed on each other and atleast two wiring layers are electrically connected to each other throughone or more holes penetrating the circuit board, comprising:

subjecting a conductive paste of the present second invention to any ofultraviolet ray irradiation, electron ray irradiation and heatingoperation, thereby dissociating the sulfur-containing compound from thesurface of the metallic particles;

filling the conductive paste in one or more holes of the circuit board;and

causing the dissociated sulfur-containing compound to operate thehardening agent, thereby hardening the resin, wherein the above stepsare performed in the above sequence.

Such a method has an advantage which is similar to the method of thethird aspect of the present invention. When the conductive pastecontaining the nano-sized metallic particles is used in the abovemethod, a multilayered circuit board having at least one electricconnections among superposed wiring layers having low and stableconnection resistivity can be provided.

Further, the multilayered circuit board can be prepared by a methodcomprising:

filling the present conductive paste in holes of the circuit board;

subjecting the conductive paste to heating operation, therebydissociating the sulfur-containing compound from the surface of themetallic particles; and

causing the dissociated sulfur-containing compound to operate thehardening agent, thereby hardening the resin, wherein the above stepsare performed in the above sequence.

In accordance with the fifth aspect of the present second invention,there is provided a method of preparing an “electric-component mountedbody” having one or more circuit boards to which one or more electriccomponents are mounted, comprising:

applying the conductive paste of the present second invention to acircuit board in a pattern corresponding to the desired circuit wiringpattern;

subjecting the conductive paste to any of ultraviolet ray irradiation,electron ray irradiation and heating operation, thereby dissociating thesulfur-containing compound from the surface of the metallic particles;

arranging one or more electric components on the circuit board so thatthe electric components contact with the conductive paste; and

causing the dissociated sulfur-containing compound to operate thehardening agent, thereby hardening the resin, wherein the above stepsare performed in the above sequence.

Such a method has an advantage which is similar to the method of thesecond aspect of the present invention. When the conductive pastecontaining the nano-sized metallic particles is used in the abovemethod, an electric-component mounted body having bonding portionshaving low and stable wiring resistivity can be provided.

In accordance with the sixth aspect of the present second invention,there is provided a method of preparing an electric-component mountedbody having one or more circuit boards to which one or more electriccomponents are mounted, comprising

subjecting the conductive paste of the present second invention to anyof ultraviolet ray irradiation, electron ray irradiation and heatingoperation, thereby dissociating the sulfur-containing compound from thesurface of the metallic particles;

applying the conductive paste to a circuit board in a patterncorresponding to the desired circuit wiring pattern;

arranging one or more electric components on the circuit board so thatthe electric components contact with the conductive paste; and

causing the dissociated sulfur-containing compound to operate thehardening agent, thereby hardening the resin, wherein the above stepsare performed in the above sequence.

Such a method has an advantage which is similar to the method of thethird aspect of the present invention. When the conductive pastecontaining the nano-sized metallic particles is used in the abovemethod, an electric-component mounted body having connecting portionshaving low and stable wiring resistivity can be provided.

The third invention of the present application is characterized in thateach of the bonding material of the first invention and the conductivepaste of the second invention further contains a fragrance material.

The conductive bonding material of the third invention is characterizedin that it has a conductive particle ingredient as the metallicparticles and the fragrance material has a reducing ability.

In the sealing agents or the adhesives of two-component epoxy resincontaining epoxy resins as the main ingredient, the problems relating tobad stench from the compounds having a thiol group (or a mercapto group)are discussed. For example, a method of masking the bad stench from thethiol group by adding vanillin, lemon oil and/or ester-based solvents(for example, see Japanese Patent Kokai Publication No. 04/23882) or amethod of absorbing low molecular weight mercaptans being the bad stenchingredients by Sepiolite which is hydrated magnesium silicate mineral(for example, see Japanese Patent Kokai Publication No. 10/60097) areproposed.

Comparing with the above adhesives of two-component epoxy resin, whenthe conductive paste of one-component epoxy resin is used, the problemsrelating to the bad stench are diluted since mixing treatment is notrequired when it is used. However, the problems are not completelydissolved.

The inventors have completed the present invention as a result ofextensive and intensive efforts, while paying attention to the maskingof the bad stench.

In accordance with the first aspect of the present third invention,there is provided a conductive paste comprising metallic fillers, resinand a hardening agent for hardening the resin, and a fragrance material.

In the conductive paste in the present third invention, bad stench canbe masked by the perfume from the fragrance material although the resinand/or hardening agent emanates bad stench since the fragrance materialis added to the conductive paste. Thus, uncomfortable sense that theoperator feel are decreased, rather preferably, the operator can feelcomfortable sense by using the conductive paste.

Further, according to the conductive paste of the third invention, theperfume is emanated from the fragrance material before the hardeningreaction is completed, however no or little perfume is emanated from theresin after the hardening reaction is completed. Thus, the operator canconfirm completion of the hardening reaction based on the absence of theperfume (or the extent of the strength of the perfume) from the paste byhis olfactory perception or any detecting machine, even if theconductive fillers are not transparent.

In the present third invention, the term fragrance material (or fragrantingredient) means the materials which emanate good perfume (or diffusean aroma) and give pleasant feeling to a human by stimulating hisolfactory perception as generally acknowledged. The fragrance materialmay contain, in addition to the ingredient emanating fragrant or aroma,i.e. fragrant ingredient, the other ingredient. Further, the fragrancematerial may be natural fragrance material or synthetic fragrancematerial, or blended fragrance material which is made by combining twoor more fragrance materials of the group consisting of natural fragrancematerials and synthetic fragrance materials.

The natural fragrance materials comprise a fragrant oil (essential oil)which is extracted from bodies of animals and/or botanicals. Examples ofanimal natural fragrance materials are musk, civet, castoreum andambergris, wherein each fragrant ingredient thereof is muscone,civetone, castoreum and ambrein. The botanical natural fragrancematerial mainly consists of fragrant oils obtained from flowers, fruits,tree bark or leaves of plants. Examples thereof are anise oil, orangeoil, cassia oil, clove oil, sandalwood oil, citronella oil, camphor oil,spearmint oil, geranium oil, turpentine oil, pine oil, peppermint oil,petitgrain oil, bergamot oil, bois de rose oil, eucalyptus oil, limeoil, Lavender oil, lemon class oil and lemon oil, wherein each fragrantingredient thereof is, for example, anethole, eugenol, cadinene,carvone, coumalin, geraniol, acetate esters (for example, cinnamylacetate, linalol acetate, menthyl acetate), safrole, methyl salicylate,santalol, citral, citronellal, cineole, camphor, cinnamic aldehyde,terpineol, decyl aldehyde, vanillin, alpha-pinene, beta-pinene, myrcene,menthol, menthone, linalool and limonene.

On the other hand, examples of the synthetic fragrance materials containionone, hydroxycitronellal, heliotropine, beta-naphthol methyl ether,gamma-undecalactone, gamma-nonalactone, methylphenylglycide acid ethyl,maltol, cyclotene, ethylmaltol, vanillin and ethylvanillin (orbourbonal), each of which may be used solely or as a mixture of two ormore.

In one embodiment of the conductive paste of the present thirdinvention, the resin is an epoxy resin and the hardener agent is acompound which has a thiol group. Those conductive paste has anadvantage that it hardens quickly at a relatively low temperature andthat the bad stench particularly emanated from the compound having athiol group can be masked by the fragrance materials. Therefore, thepresent conductive paste can be used in the appliances that are used inhuman's living environment such as electric/electronic componentswherein bad stench is an unfavorable problem, for example, portabledevices, devices used for processing or preservation of foods anddevices used for health and beauty.

In a preferable embodiment of the present third invention, theconductive filler is metallic particles, and the fragrance materialcontains an ingredient which has a reducing ability (hereinafter, merelyalso referred to as “reducible ingredient”). The metallic particles canbe oxidized by air and so on and can be sulfurated by the compoundhaving a thiol group. In such case, the material produced through thehardening of the conductive paste shows higher volumetric resistivitycompared with the material in which the surface of the metallicparticles is not coated with oxides and/or sulfide. On the other hand,in accordance with the above-mentioned embodiment of the present thirdinvention, oxidation and/or sulfurization of the surface of the metallicparticles can be prevented by adding reducible ingredients containingthe fragrance material to the conductive paste, so that increasing thevolumetric resistivity of the hardened product due to the oxidationand/or sulfurization can be avoided. The “metallic particles” used inthe present third invention may be particles consisting of a single kindof metal or alloys of such as soldering materials, preferably thelead-free soldering materials.

However, the present third invention is not limited to the abovematters. For example, the conductive fillers may be not only metallicparticles, but also particles of powders made of carbon and also theother conductive polymer. As the resin, not only epoxy resin but alsophenol resin may be used. The hardening agent may be selected from forexample amine-based compounds or phenol-based compounds other thanthiol-based compounds depending on the resin to be used. Further, theconductive paste of the present third invention can comprise, inaddition to the conductive fillers, the resin, the hardening agent andthe fragrance material, any other optional ingredient.

In the conductive paste of the present third invention, the ratio of theconductive fillers, the resin, the hardening agent, the fragrancematerial and the optionally added ingredient are selected so that theconductive fillers come to contact with each other or get closer to eachother to exhibit sufficient conductivity after the resin volumetricallyshrinked and hardened. In particular, the ratio of the fragrancematerial may be selected depending on the kind and the level (orstrength) of the stench from the ingredient emanating bad stench to bemasked, as well as the kind and the level of the perfume of thefragrance material.

The present conductive paste can be prepared by any suitable methods,for example, by merely mixing or kneading the constituent materials.

The conductive paste of the present third invention as explained in theabove can be used for various applications, for example, as the materialfor bonding materials for forming mounted electric components; forforming a circuit-wiring pattern on a circuit board; and for formingconductive connections among a plurality of circuit wiring patterns on aplurality of circuit boards.

In accordance with another aspect of the present third invention, thereis provided a method of preparing an electrical/electronic device havingcircuit boards, which boards are equipped with conductive hardenedproducts formed from a conductive paste through hardening of the resiningredient contained in the conductive paste, comprising:

(a) applying the conductive paste of the present third invention to acircuit board at a desired region thereof;(b) hardening the resin ingredient in the conductive paste by ahardening agent;(c) checking presence or absence of perfume of a fragrance materialcontained in the conductive paste in order to confirm completion of thehardening reaction, wherein the above steps are performed in the abovesequence.

According to the preparing method of the present third invention, thehardening reaction of the conductive paste is not completed while theperfume of the fragrance material is present. When the perfume of thefragrance material disappears, the operator can determine that thehardening reaction of the conductive paste is completed. Accordingly,the operator can easily determine completion of the hardening reactionrather than the case where completion of the hardening reaction isdetermined by the change of the color tone. Therefore, it is possible toestablish a method of preparing an electrical/electronic device havingimproved quality reliability.

When the operator determines that, the perfume of the fragrance materialstill remains, the hardening reaction is not completed. Thus, it ispreferable for the operator to repeat the steps (b) and (c) in the abovemethod until the perfume of the fragrance material disappears.

In accordance with another aspect of the present third invention, thereis provided an electrical/electronic device equipped with conductivehardened products formed from a conductive paste of the present thirdinvention through hardening of the resin ingredient contained in theconductive paste. Those devices have an advantage of improved qualityreliability. The electrical/electronic device of the present thirdinvention comprises for example an electric-component mounted bodywherein one or more electric components are mounted on a circuit boardby the conductive hardened products. Further, the electrical/electronicdevice of the present third invention comprises a circuit board on whichconductive hardened products functions as the circuit wiring pattern, aswell as a multilayered circuit board, wherein a plurality of wiringlayers are superposed on each other and at least two wiring layers areelectrically connected to each other with the conductive hardenedproducts filling one or more holes penetrating the circuit board.

EFFECT OF THE INVENTION

In accordance with the first invention of the present application, thereis provided a bonding material for preparing a mounted body which canharden at a relatively low temperature and has a improved preservationstability since the bonding material contains a sulfur-containingcompound, in particular a reforming agent containing a —SH group whichcauses the epoxy resin to start hardening reaction in a suitable amount.Further, a method of preparing circuit boards using the bonding materialfor preparing a mounted body and an electrical/electronic device havingsuch circuit boards are also provided.

In accordance with the second invention of the present application,there is provided a conductive paste containing a coordinatablesulfur-containing compound, which makes coordinate bond at the end groupthereof with the surface of the metallic particles and which functionsas hardening agent for the resin when the end group dissociates from thesurface of the metallic particles. The state of the coordinated bond ofthe sulfur-containing compound can be controlled so as to show animproved preservation stability when it is preserved and to causehardening reaction only when it is desired. In particular, when acoordinatable sulfur-containing compound which functions as a quick andlow temperature-hardening agent at the dissociated state is used, aconductive paste which hardens quickly at a low temperature and shows ahigh preservation stability is realized.

Further, in accordance with the second invention of the presentapplication, there is provided a method of preparing a circuit board, amultilayered circuit board and an electric-component mounted body usingthe conductive paste as mentioned in the above. Those methods have anadvantage that the handling of the conductive paste is easy. Inaddition, each of the circuit board, the multilayered circuit board andthe electric-component mounted body that were prepared using the abovemethods has an advantage that the connection resistivity of eachconnection of the circuit board, the multilayered circuit board and theelectric-component mounted body is low.

In accordance with the third invention of the present application, thereis provided a conductive paste containing a fragrance material, therebyit is possible to reduce or kill bad stench and it is easily determinedto confirm completion of the hardening reaction. In particular, epoxyresin and a compound having a thiol group as the hardening agent areused in one-component conductive paste which can harden at a relativelylow temperature, the bad stench emanated from the compound having athiol group can be masked by the perfume from the fragrance material.Accordingly, the conductive paste may be used for broad applications,for example, the portable devices, the devices used for processing orpreservation of foods and the devices used for health and beauty.

In accordance with the method of preparing the electrical/electronicdevice of the invention of the present application, completion of thehardening reaction can be easily determined on the basis of the presenceor absence of the perfume of the fragrance material by using theconductive paste of the third invention. Therefore, it is possible toprepare an electrical/electronic device having high quality reliability.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic view of the conductive paste in the thirdembodiment of the second invention.

FIG. 2 is a schematic flow sheet of cross sectional view of preparing acircuit board in the forth embodiment of the second invention.

FIG. 3 is a schematic flow sheet of cross sectional view of preparing acircuit board in the fifth embodiment of the second invention.

FIG. 4 is a schematic flow sheet of cross sectional view of preparing amultilayered circuit board in the sixth embodiment of the secondinvention.

FIG. 5 is a schematic flow sheet of cross sectional view of preparing anelectric-component mounted body in the seventh embodiment of the secondinvention.

FIG. 6 is a schematic flow sheet of cross sectional view of preparing anelectric-component mounted body in the eighth embodiment of the secondinvention.

EXPLANATION OF REFERENCE NUMERALS

-   -   1: first metallic particle; 2: a sulfur-containing compound; 3:        a compound coordinated with metal; 4: resin; 5: second metallic        particle; 6, 6′: board; 7: conductive paste; 7′: conductive        hardened product; 8: mask; 9: squeegee; 10: ultraviolet ray or        electron ray; 11: hole; 12 a, 12 b: wiring layer; 13: circuit        board; 14: an electric components.

First Embodiment First Invention

The present embodiment relates to a bonding material for preparing amounted body (or conductive adhesive).

The bonding material in the present embodiment is one-componentcomposition comprising an epoxy resin ingredient, a latent hardeningagent for hardening the epoxy resin, a conductive particle ingredientand a sulfur-containing compound. Although it is not indispensableingredient, the present bonding material preferably contains the otheringredient such as thickening agent.

The bonding material contains the sulfur-containing ingredient about1-100 parts by weight, preferably about 2-80 parts by weight based on100 parts by weight of the epoxy resin. As to the other ingredients,without being limited to, for example, the bonding material may containabout 0.1-30 parts by weight of the latent hardening agent, about100-1000 parts by weight of the conductive particles, and optionallyabout 0.5-25 parts by weight of the thickening agent (each based on 100parts by weight of the epoxy resin).

It is possible to use un-hardened epoxy resin, i.e. a resinous materialhaving two or more epoxy groups in one molecule as the epoxy resin. Forexample, epoxy resins which are known in the prior art, such as glycidylether type epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins and cyclic aliphatic type epoxy resins may beused. Alternatively, the precursors of such compounds may be also used.

The latent hardening agent for hardening the epoxy resin is a hardeningagent having functions that, when contained in one-component epoxy resinmaterial (also containing epoxy resin and its hardening agent), theepoxy resin material can be preserved at room temperature (e.g. about15-30 degree centigrade) for a long time period without changing theproperty and when heated to a predetermined temperature, it quicklycauses the epoxy resin to harden. Examples of the latent hardening agentto be applicable to the first invention are, for example, dicyandiamide,organic acid dihydrazide, amineimide, tertiary amine salt, imidazolesalt, salts of Lewis acid and Bronsted acid, preferably latent hardeningagent having an amine structure in the molecule thereof (for example,see “epoxy resin handbook”, edited by Niiho Masaki, Nikkan KogyoShinbun-sya, pp. 225-230).

As the conductive particles, any materials having electroconductivity byitself may be used. For example, particles made of metals such as gold,silver, copper, nickel, silver-palladium alloy and solder alloy, orparticles made of the other conductive materials such as carbon can beused. Although the shape and the size of the conductive particles arenot particularly limited, the particles may have a number averageparticle size in a range for example from 0.1 to 50 micrometer.

In the first invention, the term “reforming agent” means one or morecompounds that affects at least one of the epoxy resin and theconductive particles to reform the property thereof, for example, toimprove the adhesion strength thereof. The reforming agent which isapplicable to the first invention has such functions and further has oneor more of —SH groups in the molecule. The sulfur-containing compoundalso being such a reforming agent having one or more of —SH groups inthe molecule can lower the hardening temperature thereof due to thepresence of the latent hardening agent.

Examples of the sulfur-containing compounds contain mercapto-propionicacid derivatives (for example, 3-mercapto-propionic acid, methoxybuthylmercaptopropinate, octyl mercaptopropinate, tridecyl mercaptopropinate,trimethylolpropane tris(mercaptopropionate) and pentaerythritoltetrakis-thiopropionate); thioglycol acid derivatives (for example,thioglycol acid, ammonium thioglycolate, monoethanolamine thioglycolate,methyl thioglycolate, octyl thioglycolate, methoxybuthyl thioglycolate,ethyleneglycol bisthioglycolate, butanediol bisthioglycolate,trimethylolpropane tris(thioglycolate), pentaerythritoltetrakis(thioglycolate)); and thiols (thiomalic acid, stearyl mercaptan,2-mercapto-ethyloctanoate ester, 4-mercaptopyrizine, 2-mercaptopropionicacid.

Alternatively, a sulfur-containing compound which does not have a —SHgroup, but can produce a —S— group may be used as the sulfur-containingcompound. For example, thiirane and cyclic or linear thiiranederivatives (for example, salts and complexes of thiirane) can attainthe same effects in the first invention.

As the thickening agent, typical inorganic thickening materials (orthixotropic agent) can be used. Further, the other optional additives,e.g. hardening promoting agents, fillers, pigments, dyes, flexibilityadding agent and dispersants can be optionally added.

The bonding material for preparing a mounted body of the presentembodiment can be prepared by appropriately mixing or kneading theconstituent materials.

The bonding material of the present embodiment is grasped as aconductive adhesive and is understood that it do not show anyelectroconductivity before it hardens. However, when the bondingmaterial is heated, the epoxy resin volumetrically shrinks and hardens,so that the conductive particles therein come to contact one another orget closer to each other, thereby shows electroconductivity. Since thebonding material of the present embodiment contains a sulfur-containingcompound, which causes hardening of the epoxy resin at a proper amount,the present bonding material can be stably preserved for relatively longtime, at least over seven days. In addition, the present bondingmaterial can harden at a relatively low temperature, particularly at atemperature in a range from 70 to 110 degree centigrade.

Second Embodiment First Invention

The present embodiment relates to the method of preparing circuit boardsand electric/electronic devices containing such circuit boards.

First, a bonding material of the first invention as mentioned in theabove first embodiment is applied to the electrode (or land) of a board.The bonding material can be applied by any of various methods, forexample, transfer printing, screen printing or dispensing. A board,which is generally known in the technical field, comprises an insulatingboard (substrate) and a circuit-wiring pattern, wherein thecircuit-wiring pattern is integrally formed on the board can be used.

Next, an electric component is arranged onto the circuit board so thatthe electrodes of the electric component are suitably aligned with andcontacted with the bonding material on the board.

Then, the obtained board is subjected to heating, for example by passingthrough a reflow oven, thereby the bonding material is maintained at atemperature condition in a range between 70 to 110 degree centigrade forsuitable period of time, for example from 0.5 to 10 minutes. As aresult, the epoxy resin sufficiently hardens to bond the electrode ofthe board with the electrode of the electric component, and thereby theconductive particles therein come to contact one another or get closerto each other to show electroconductivity. Accordingly, the electriccomponent can be mechanically and electrically bonded with the electrodeof the board by the hardened adhesive.

The electric component used in the present embodiment is sufficient tohave an allowable temperature limit which is higher than the heatingtemperature. For example, an electric component having an allowabletemperature limit lower than 120 degree centigrade may be used in thepresent embodiment as far as its allowable temperature limit is higherthan the heating temperature. The heating temperature may beappropriately set in a temperature range from 70 to 110 degreecentigrade considering the allowable temperature limit of the electriccomponent so as to obtain sufficient hardening.

A circuit board to which electric components are mounted is preparedaccording to the above method.

Such circuit board can be used by being built-in variouselectrical/electronic devices. Examples of such electrical/electronicdevices are as follows:

Portable electronic devices such as video-camera, portable CD, portableMD, portable DVD, mobile phone and laptop computer;

Typically stationary settled electronic devices such as stereo set,desk-top type computer, video telephone, DVD player, CD player, DVDrecorder, CD recorder and television set;

Home appliance electronic devices such as rice cooking device, microwaveoven, refrigerator, cleaner, washing machine, air conditioner, lightingapparatus, intercom, security camera, monitoring camera, gas leakagedetector and the toilet seat with the washing functions;

Electronic devices for vehicles, for example for automobile andtwo-wheeled motor vehicle, such as car stereo, car navigation system,car air-conditioner, car sensor, engine controller, loading camera,automatic brake safe control system (ABS) and headlight.

Second Invention

Hereinafter, various embodiments of the second invention are illustratedin detail with reference to FIGS. 1-6. In the embodiment relating to thesecond invention, similar members are denoted with the same referencenumerals. Unless particularly mentioned, an explanation of one member inone embodiment is also applicable to the other member in the otherembodiment.

Third Embodiment Second Invention

The present embodiment relates to a conductive paste, a method ofpreparing the conductive paste and a method of using the same in onepreferred embodiment of the second invention.

As shown in FIG. 1( a), the conductive paste 7 of the present embodimentcomprises a first metallic particles 1, a coordinatablesulfur-containing compound 2 and an insulating resin 4. Thecoordinatable sulfur-containing compound 2 coordinates at the end groupthereof with the surface of the first metallic particles 1 to form metalcoordination compounds 3.

The end group of the coordinatable sulfur-containing compound 2coordinating with the first metallic particles 1 may be for example athiol group and the sulfur atom therein performs as a coordinating atom.The resin 4 may be for example an epoxy resin. Since the thiol grouprelates to hardening of the epoxy resin, the coordinatablesulfur-containing compound 2 functions as the hardening agent for theresin 4 when the end group of the coordinatable sulfur-containingcompound 2 dissociates from the surface of the metallic particles 1.

The first metallic particles 1 may consist of any of gold, silver orcopper. The thiol group (particularly, sulfur atom) of the coordinatablesulfur-containing compound 2 can suitably coordinate with such metallicparticles. The mean particle diameter of the first metallic particles 1may be, for example, in a range from about 1 nm to 100 μm and preferablyin a range from about 1 to 100 nm. When the first metallic particles 1were nano-size particles, they can be dispersed in the resin 4 due tothe coordination of the coordinatable sulfur-containing compound 2thereto. Although merely several particles of resin 4 are imaginarilyshown in FIG. 1, there are a lot of particles or constituent elements ofresin 4 in the practical reacting system of the conductive paste. Thus,the imaginarily shown particles or constituent elements of resin 4 playa role as dispersion medium.

The conductive paste 7 of the present embodiment may further containsecond metallic particles 5 as shown in FIG. 1( a). The second metallicparticles 5 may consist of for example gold, silver, copper, platinum,palladium, rhodium, osmium, ruthenium, iridium, iron, zinc, cobalt,nickel, chromium, titanium, tantalum, indium and silicon. Thecoordinatable sulfur-containing compound 2 may coordinate with thesecond metallic particles 5 or not. The mean particle diameter of thesecond metallic particles 5 may be, for example, in a range from about0.1 to 100 μm, and in particular in a range from 0.1 to 20 μm. However,the conductive paste of the second invention may not contain the secondmetallic particles 5, without being limited to the above explanation.

In the context of the present specification, the term “mean particlediameter” means a number average particle diameter of the aggregation ofthe particles. It can be measured by a laser diffraction (lightscattering) method, for example using Microtrac particle size analyzers9320 HRA (available form NIKKISO CO., LTD., Tokyo, Japan).

In the present embodiment, the conductive paste 7 contains the firstmetallic particles 1, the coordinatable sulfur-containing compound 2,the resin 4 and the second metallic particles 5 if present, in a ratiofor example of about 100 parts by weight of the first metallic particles1, about 60-95 parts by weight of the coordinatable sulfur-containingcompound 2, about 30-2 parts by weight of the resin 4 and about 30-2parts by weight of the second metallic particles 5 if present. Withoutbeing limited to the above, the ratio of each ingredient of the presentsecond invention may be selected optionally.

The present conductive paste may further contain the other ingredientsas needed, for example hardening promotor, filler, extender, solvent,pigment, plasticity additive and dispersant at an adequate amount.

The conductive paste 7 in the present embodiment can be prepared bymixing the first metallic particles 1 having an exposed surface with thecoordinatable sulfur-containing compound 2 to form the metalcoordination compounds 3, and then insulating resin 4 is added and mixedwith the metal coordination compounds 3. The second metallic particles 5(as well as the other optional ingredients) may be mixed simultaneouslywith the first metallic particles 1 and the coordinatablesulfur-containing compound 2 or may be added to the mixture togetherwith the resin 4.

Next, the method to use the above conductive paste 7 is explained.

When an external influences, for example, irradiation of ultraviolet rayor electron ray or heating is applied to the conductive paste 7, thecoordinate bond between the first metallic particles 1 and the endgroups of the sulfur-containing compound 2 is broken. Thus, the metalcoordination compound 3 is dissolved and the sulfur-containing compound2 dissociates from the surface of the metallic particles 1 as shown inFIG. 1( b). When ultraviolet ray or electron ray is irradiated, theirradiation dose may be optionally adjusted, and the temperature of theconductive paste 7 and the board 6 may increase slightly. When heatingis applied, the conductive paste 7 and the board 6 may be heated at atemperature from 60 to 120 degree centigrade for about 5 to 60 minutes,but it is not limited thereto.

The dissociated sulfur-containing compound 2 can operate as thehardening agent for the resin. For example, when heating is applied, itcauses the resin 4 to harden as shown in FIG. 1( c) without additionaloperation. When the resin 4 is epoxy resin and the end group of thesulfur-containing compound 2 is a thiol group, for example, the resinhardens by maintaining the temperature from about 80 to 120 degreecentigrade for about 5 to 60 minutes. Alternatively, the resin hardensby irradiation of ultraviolet ray or electron ray.

When a heating operation is performed to harden the resin 4, thisoperation can be performed at a condition different from the operationto dissociate the sulfur-containing compound 2. However, if it isappropriate, both operations can be combined with together or performedin sequence.

As a result, the epoxy resin 4 volumetrically shrinks and hardens, sothat the metallic particles 1 therein come to contact one another or getcloser to each other, thereby a hardened product 7′ which showselectroconductivity as a whole is formed.

In particular, when the mean diameter of the metallic particles 1 is ina range from about 1 to 100 nm, the metallic particles 1 sinter oneanother upon dissociating the sulfur-containing compound 2 and/orhardening of the resin 4 by being heated at a temperature from about 25to 110 degree centigrade for about 2 to 30 minutes. Thus, the obtainedconductive hardened product 7′ shows very low resistivity. In addition,since the metallic particles 1 are sintered one another, the resistivityof the conductive hardened product 7′ is substantially not influenced bythe volume change of the hardened resin 4 due to a temperature change.

Thus, according to the conductive paste, of the present embodiment, itis possible to attain a high stability when preserved and to causeharden only when desired. The conductive paste of the present embodimentmay form a conductive hardened product by using at a relatively lowtemperature. Further, the resistivity of the obtainable hardened productmay be further lowered and stabilized by using nano-size metallicparticles as the conductive paste and sintering them.

Fourth Embodiment Second Invention

The present embodiment relates to a method of preparing a circuit boardin one embodiment of the second invention.

First, an insulated board (or substrate) 6 is provided, as shown in FIG.2( a). Any material selected from polyethylene terephthalate,polyethylene naphthalate, polycarbonate, polyimide, thermoplastic resin,aramide nonwoven and glass nonwoven may be used as the board 6, but itis not limited thereto.

Then, as shown in FIG. 2( b), for example the conductive paste 7 asmentioned in the first embodiment is applied to the board 6 in a patterncorresponding to the desired circuit wiring pattern. Any method selectedfrom screen printing, ink-jet printing, dispensing by dispenser,impregnation, spin-coating may be applicable. FIG. 2( b) schematicallyshows a screen printing method, wherein squeegee 9 is pressingly movedover a mask 8, so that the conductive paste 7 is printed on the board 6through openings of desired pattern in the mask 8. After printed, themask 8 is removed from the board 6.

Then, the conductive paste 7 on the board 6 is irradiated withultraviolet ray or electron ray 10 or the conductive paste 7 is heatedtogether with the board 6. Thus, the sulfur-containing compoundcoordinated with the surface of the metallic particles in the conductivepaste 7 dissociates from the surface of the metallic particles.

Then the resin is hardened by causing the dissociated sulfur-containingcompound to operate the hardening agent, thereby a hardened product 7′is obtained as shown in FIG. 2( d). It is preferable that the resinhardens quickly at a relative low temperature. For example, in the casewhere heating operation is required, the hardening preferably startsafter the dissociation without any additional operation.

As explained in the above, a circuit board having a circuit wiringpattern made of the conductive hardened product 7′ on the surface ofsaid board 6 is prepared.

According to the method of preparing circuit board in the presentembodiment, since the conductive paste of the second invention is usedas the material for preparing the circuit wiring pattern, a goodpreservation stability is attained and easier handling duringpreparation is also attained. In addition, it is after the conductivepaste was applied onto the board that the sulfur-containing compounddissociates from the surface of the metallic particles. Thus, there isno danger that the resin starts to harden before or during applicationof the conductive paste to the board, so that it is not necessary to payparticular attention to handling. Further, it is possible to prepare acircuit board having a desired circuit wiring pattern at a relativelylow temperature. In addition, when the conductive paste containing thenano-sized metallic particles is used in the above method, a circuitboard having low and stable wiring resistivity can be provided.

Fifth Embodiment of the Second Invention

The present embodiment relates to a method of preparing a circuit boardin another embodiment in the present second invention. The presentembodiment is a modified version of the forth embodiment, so that thedifference from the forth embodiment is mainly explained hereinafter.

First, an insulated board (or substrate) 6 is provided, as shown in FIG.3( a).

Separately, a conductive paste 7 as explained in the first embodiment isirradiated with ultraviolet ray or electron ray 10 or the conductivepaste 7 is heated as shown in FIG. 3( b), so that the sulfur-containingcompound coordinated with the surface of the metallic particles isdissociated from the surface of the metallic particles.

Then, the above conductive paste 7 is applied to the board 6 in apattern corresponding to the desired circuit wiring pattern as shown inFIG. 3( c). In the present embodiment, it is preferable that theconductive paste 7 does not substantially start hardening reaction afterthe sulfur-containing compound was dissociated from the surface of themetallic particles and before the application completes.

Then, the dissociated sulfur-containing compound causes hardeningreaction of the epoxy resin to obtain a conductive hardened product 7′as shown in FIG. 3( d). It is preferable that the resin hardens quicklyand at a relatively low temperature. Such a hardening reaction can becaused by heating the conductive paste 7′ together with the board 6.

As mentioned in the above, a circuit board having a circuit wiringpattern made of the conductive hardened product 7′ on the surface ofsaid board 6 is obtained.

According to the method of preparing circuit board in the presentembodiment, since the conductive paste of the second invention is usedas the material for preparing the circuit wiring pattern, a goodpreservation stability is attained and easier handling during thepreparation is also attained. In addition, since the sulfur-containingcompound has been dissociated from the surface of the metallic particlesbefore the conductive paste is applied to the board, it is not necessaryto expose the board to ultraviolet ray or electron ray or to heat theboard. Thus, it is possible to prepare a circuit board having a desiredcircuit wiring pattern at a relatively low temperature, with avoidingheating the board and devices optionally existing on the board as far aspossible. In addition, when the conductive paste containing thenano-sized metallic particles is used in the above method, a circuitboard having low and stable wiring resistivity can be provided.

Sixth Embodiment of the Second Invention

The present embodiment relates to a method of preparing a multilayeredcircuit board, in particular a double sided circuit board in oneembodiment of the second invention.

First, a substrate 6′ having a penetrating hole 11 at an adequateposition is provided, as shown in FIG. 4( b). This substrate 6′ is thesame as that of the above forth embodiment and to which substrate a hole11 is formed through machining processing such as drilling or punchingor thermal processing such as laser irradiation.

Separately, a conductive paste 7 as explained in the first embodiment isirradiated with ultraviolet ray or electron ray 10 or the conductivepaste 7 is heated as shown in FIG. 4( b), so that the sulfur-containingcompound coordinated with the surface of the metallic particles isdissociated from the surface of the metallic particles.

Then, the above conductive paste 7 is applied to the hole 11 of theboard 6′ as shown in FIG. 4( c). Any method selected from screenprinting, ink-jet printing, dispensing by dispenser, impregnation,spin-coating may be applicable to fill the hole 11. FIG. 4( c)schematically shows a screen printing method. In the present embodiment,it is preferable that the conductive paste 7 does not substantiallystart hardening reaction after the sulfur-containing compound wasdissociated from the surface of the metallic particles and before theapplication completes

Then, the dissociated sulfur-containing compound causes hardeningreaction of the epoxy resin to obtain a conductive hardened product 7′.It is preferable that the resin hardens quickly and at a relatively lowtemperature. Such a hardening reaction can be caused by heating theconductive paste 7′ together with the board 6.

Then, as shown in FIG. 4( e), a wiring layer 12 a is formed on the topside of the substrate 6′ and another wiring layer 12 b is formed on thebottom side of the substrate 6′. The wiring layer 12 a is electricallyconnected with the wiring layer 12 b via the conductive hardened product7′ which fills the through hole 11. Each wiring layer can be formedaccording to the methods explained in the above second or thirdembodiment. Alternatively, a method to form a wiring layer which isknown in the prior art can be also applicable.

As above mentioned, a multilayered circuit board having wiring layers 12a and 12 b on both sides of the board 6 and the conductive hardenedproduct 7′ forming a conductive path between both wiring layers 12 a and12 b is obtained.

According to the method of preparing circuit board in the presentembodiment, since the conductive paste of the second invention is usedas the material for preparing the circuit wiring pattern, a goodpreservation stability is attained and easier handling during thepreparation is also attained. In addition, since the sulfur-containingcompound is dissociated from the surface of the metallic particlesbefore the conductive paste fills the hole of the board, it is notnecessary to expose the board to ultraviolet ray or electron ray or toheat the board. Thus, it is possible to prepare a circuit board having adesired circuit wiring pattern at a relatively low temperature, withavoiding heating the board and devices optionally existing on the boardas far as possible. In addition, when the conductive paste containingthe nano-sized metallic particles is used in the above method, amultilayered circuit board having an electric connections having low andstable wiring resistivity can be provided.

In the above embodiment, a multilayered circuit board, in particular adouble sided circuit board wherein two wiring layers are arranged onboth sides of the board is explained. However, a multilayered circuitboard having more layers, wherein each layer has two wiring layers onboth sides can be obtained by a method which is similar to the methodexplained in the present embodiment. Although the wiring layers 12 a and12 b were formed on the board 6′ after the hole 11 was filled with theconductive paste 7 In the present embodiment, filling the conductivepaste 7 can be performed after forming both wiring layers 12 a and 12 bon the board 6′.

In the present embodiment, the conductive paste is irradiated withultraviolet ray or electron ray or the conductive paste is heatedtogether with the board, and then such a conductive paste is filled inthe hole which was formed on the board. However, in the case where thedissociation is caused by heating, untreated conductive paste is filledin the hole of the board, and then the conductive paste can be heatedtogether with the board, thereby the sulfur-containing compoundcoordinated with the surface of the metallic particles in the conductivepaste can be dissociated from the surface of the metallic particles.Thus, the dissociated sulfur-containing compound may perform ashardening agent to obtain a hardened resin.

Seventh Embodiment Second Invention

The present embodiment relates to a method of preparing anelectric-component mounted body in one embodiment of the secondinvention.

First, a circuit board 13 is provided as shown in FIG. 5( a) (whereinany wiring layer is not shown). The circuit board 13 can be formedaccording to the methods explained in the above second or thirdembodiment or can be formed by a method which is known in the prior artor can be commercially available one.

Next, the conductive paste 7 explained in the above first embodiment isapplied to the circuit board 13 at a desired region, for example tolands (not shown) which are electrically connected with any wiring layeras shown in FIG. 5( b). The method used in the forth embodiment can beadopted as the applying method. FIG. 5( b) schematically shows a screenprinting method.

Then, the conductive paste 7 on the board 13 is irradiated withultraviolet ray or electron ray 10 or the conductive paste 7 is heatedtogether with the board 13. Thus, the sulfur-containing compoundcoordinated with the surface of the metallic particles in the conductivepaste 7 dissociates from the surface of the metallic particles.

Next, an electric component 14 is arranged onto the circuit board 13 sothat the electric component is suitably aligned with and contacted withthe conductive paste 7 on the board 13.

Then the resin is hardened by causing the dissociated sulfur-containingcompound to operate the hardening agent, thereby a conductive hardenedproduct 7′ is obtained as shown in FIG. 5( d). It is preferable that theresin hardens quickly at a relative low temperature. For example, in thecase where heating operation is required, the hardening preferablystarts after the dissociation without any additional operation.

As a result, the electric component 14 is mechanically andelectronically bonded to the wiring circuit board 13 by means of theconductive hardened products 7′ which is arranged between the wiringcircuit board 13 and the electric component 14, so that the electriccomponent 14 is mounted on the circuit board 13.

As explained in the above, an electric-component mounted body havingbonding portions (or connecting regions) wherein the conductive hardenedproduct 7′ forms the connecting regions mounting the electric component14 on the circuit board 13 can be prepared.

According to the method of preparing the electric-component mounted bodyin the present embodiment, since the conductive paste of the secondinvention is used as the material for bonding material for mounting,good preservation stability is attained and easier handling during thepreparation is also attained. In addition, it is after the conductivepaste was applied onto the board that the sulfur-containing compounddissociates from the surface of the metallic particles. Thus, there isno danger that the resin starts to harden before or during applicationof the conductive paste to the board, so that it is not necessary to payparticular attention to handling. Further, it is possible to prepare acircuit board having a desired circuit wiring pattern at a relativelylow temperature. In addition, when the conductive paste containing thenano-sized metallic particles is used and sintered in the above method,an electric-component mounted body having conductive connections havinglow and stable bonding resistivity can be provided.

Eighth Embodiment Second Invention

The present embodiment relates to a method of preparing anelectric-component mounted body in another embodiment of the secondinvention. This embodiment is a modified version of the seventhembodiment, so that the difference from the seventh embodiment is mainlyexplained hereinafter.

First, a circuit board 13 is provided, as shown in FIG. 6( a).

Separately, a conductive paste 7 as explained in the first embodiment isirradiated with ultraviolet ray or electron ray 10 or the conductivepaste 7 is heated as shown in FIG. 6( b), so that the sulfur-containingcompound coordinated with the surface of the metallic particles isdissociated from the surface of the metallic particles.

Then, the above conductive paste 7 is applied to the board 13 at desiredregions, for example to the lands (not shown) which is electricallyconnected with the wiring layer as shown in FIGS. 6( c) and (d). In thepresent embodiment, it is preferable that the conductive paste 7 doesnot substantially start hardening reaction after the sulfur-containingcompound was dissociated from the surface of the metallic particles andbefore the application completes

Next, an electric component 14 is arranged onto the circuit board 13 sothat the electric component 14 is suitably aligned with and contactedwith the conductive paste 7 on the board 13.

Then the resin is hardened by causing the dissociated sulfur-containingcompound to operate the hardening agent, thereby a conductive hardenedproduct 7′ is obtained as shown in FIG. 6( e). It is preferable that theresin hardens quickly at a relative low temperature. For example,hardening of the resin can be caused by heating the conductive paste 7together with the circuit board 13 and the electric component 14.

As a result, the electric component 14 is mechanically andelectronically bonded to the wiring circuit board 13 by means of theconductive hardened products 7′ which is arranged between the wiringcircuit board 13 and the electric component 14, so that the electriccomponent 14 is mounted on the circuit board 13.

As explained in the above, an electric-component mounted body havingbonding portions wherein the conductive hardened product 7′ forms thebonding portions mounting the electric component 14 on the circuit board13 can be prepared.

According to the method of preparing the electric-component mounted bodyin the present embodiment, since the conductive paste of the secondinvention is used as the material for bonding material for mounting,good preservation stability is attained and easier handling during thepreparation is also attained. In addition, since the sulfur-containingcompound is dissociated before the conductive paste is applied to theboard, there is no danger that the board is exposed to ultraviolet rayor electron ray or heated for dissociation. Thus, it is possible toprepare a circuit board having a desired circuit wiring pattern at arelatively low temperature, with avoiding heating the board and devicesoptionally existing on the board as far as possible. In addition, whenthe conductive paste containing the nano-sized metallic particles isused and sintered in the above method, an electric-component mountedbody having conductive connections having low and stable bondingresistivity can be provided.

Third Invention Ninth Embodiment Third Invention

The present embodiment relates to a conductive paste in one embodimentof the present third invention.

The conductive paste of the present embodiment comprises metallicparticles which is conductive fillers, an epoxy resin, a hardening agentconsisting of a compound having a thiol group and a fragrance material.

The metallic particles may be the particles of a single kind of metalselected from the group of gold, silver, copper and nickel, or of analloy or a mixture comprising two or more kinds of the metals asmentioned in the above, or the particles of the soldering materials of,for example an Sn—Bi based alloy and Sn—Bi—In based alloy, an Sn—Agbased alloy, an Sn—Cu based alloy, an Sn—Ag—Cu based alloy, and one ormore of those alloys to which Bi and/or In is further added. The numberaverage particle size of the metallic particles is for example, fromabout 1 to 50 micrometer, preferably from about 2 to 20 micrometer.

As the epoxy resin, for example bisphenol A type epoxy resin, bisphenolF type epoxy resin and modified epoxy resins thereof may be used.

The compound having a thiol group is desirable in this invention sinceit performs as the hardening agent for the epoxy resin, in particularmakes it possible to harden quickly at a lower temperature. The examplesof such compound are for example, thioglycol acid and the derivativesthereof, mercaptopropionic acid and the derivatives thereof, thiomalicacid, mercaptopyrizine, stearyl mercaptan and mercapto-ethyloctanoateester.

As the fragrance material, for example, plant-derived natural fragrancematerials having terpene series compounds and the derivatives thereof(in particular, limonen, linalool and citral etc) as the perfumecomponent thereof, such as ionone, hydroxycitronellal, maltol, vanillinand ethylvanillin (or bourbonal) or synthetic fragrance materials may beused.

Particularly, in the embodiment wherein a compound having a thiol groupis used, it is preferable to use a fragrance material having so strongperfume that the bad stench emanated from the compound could be masked.As such a fragrance material, synthetic fragrance material or preparedfragrance material is suitable rather than plant-derived naturalfragrance materials.

In the case where the metallic particles are made of a metal which issusceptible to being sulfurized, or made of a metal which is susceptibleto being oxidized, it is preferable to use fragrance materials whichhave a reducing ability to reduce or preferably prevent thesulfurization or oxidization of the surface of the metallic particles,thus to reduce or preferably prevent the volume resistivity of theconductive hardened product from being increased, (or, which have moresusceptible ability to being sulfurized or being oxidized rather thanthe metal consisting of the metallic particles). Such fragrancematerials are for example a kind of fragrance having a carboxyl group inthe molecule, such as cinnamic acid, and a kind of fragrance having analdehyde group in the molecule, such as vanillin, ethylvanillin,heliotropine, anisaldehyde, amyl cinnamic aldehyde, cinnamic aldehyde,citral, citronellal, decyl aldehyde, hydroxycitronellal. The fragrancematerial may have an optional form, for example, generally a powder formin the case of vanillin, ethylvanillin and heliotropine, and generally aliquid form in the case of anisaldehyde, amylcinnamic aldehyde, cinnamicaldehyde, citral, citronellal, decyl aldehyde, and hydroxycitronellal.

The conductive paste of the present embodiment may contain theingredients thereof in a ratio of, for example, about 100 parts byweight of epoxy resin, about 25-600 parts by weight of the metallicparticles, about 1-100 parts by weight of the hardening agent and about1-100 parts by weight of the fragrance materials. However, the ratiothereof may be optionally selected without being limited thereto.

The conductive paste of the present embodiment may contain the otheringredients, for example hardening promotors, fillers, extenders,solvents, pigments, plasticity additives and dispersants at an adequateamount.

The conductive paste of the present embodiment can be prepared throughany optional methods, for example by merely mixing or kneading theingredients, i.e. commercially available metallic particles, epoxyresin, hardening agent, fragrance and optional additional ingredient.

When the conductive paste of the present embodiment is heated, thecompound having thiol group performs as a hardening agent for the epoxyresin, thereby the epoxy resin volumetrically shrinks and hardens, sothat the metallic particles therein come to contact one another or getcloser to each other. After sufficiently hardened, the hardened productshows an improved electroconductivity and emanates substantially noperfume.

According to the conductive paste of the present embodiment, since theparticularly bad stench emanated from the compound having a thiol groupis masked by the perfume of the fragrance material, on the one hand, thebad and unpleasant stench can be efficiently reduced, and on the otherhand, the paste can emanate pleasant perfume. In addition, since theconductive paste of the present embodiment comes not to emanate perfumewhen the hardening completes, an operator in charge of the mountingperformance can easily confirm that the hardening operation hascompleted. The conductive paste of the present embodiment can be usedfor the portable devices, the devices used for processing orpreservation of foods and the devices used for health and beauty due tothe bad stench emanated from the conventional conductive paste.

Tenth Embodiment Third Invention

The present embodiment relates to a method of preparing theelectric-component mounted body in one embodiment of the present thirdinvention.

First, a circuit board made of an insulating material, for example,polyethylene terephthalate, polyethylene naphthalate, polycarbonate,polyimide, epoxy resin, aramide nonwoven, glass woven, glass nonwoven,on at least one side of which board a circuit wiring pattern is formedwith a conductive material, for example, copper, gold, a hardenedproduct of a conductive paste is provided. A circuit board which is oneof commercially available boards or prepared through the preparingmethods known in the prior art can be used as the circuit board.

Then, the conductive paste explained in the above ninth embodiment isapplied to desired regions of the circuit board, particularly to theelectrodes (for example lands) by a screen printing method. Inparticular, a mask having one or more openings having a predeterminedpattern is arranged on the circuit board, a squeegee is pressingly movedover the mask, so that the conductive paste is printed on the boardthrough the opening in the mask. In order that the printed conductivepaste has a uniform thickness, it is preferable that the mask is a metalmask (or made of a metal) and the squeegee is made of a fluorinecontained resin. After printing, the mask is removed from the circuitboard. In stead of screen printing method, the other method for exampleink-jet printing, dispensing by dispenser, impregnation, spin-coatingcan be applicable to apply the conductive paste on the board at adesired region.

Thereafter, an electric component is arranged onto the circuit board sothat the electrodes (for example leads) of the electric component aresuitably aligned with and contacted with the bonding material on theboard. The way how to arrange may vary depending on the kinds of theelectric component. However, it may also be sufficient to merely put theelectric component on the conductive paste since the viscosity of theconductive paste decreases and the paste covers the conductiveconnections in the following heating step. It will be appreciated thatanother arrangement wherein the electric component is relatively forcedon the conductive paste, thereby causing intimate attachmenttherebetween may be adopted.

When the obtained circuit board is heated, the compound having a thiolgroup performs as the hardening agent for the epoxy resin in theconductive paste, so that the hardening of the epoxy resin completes:Heating may be performed for example at a temperature of from about 70to 200 degree centigrade, preferably from about 70 to 120 degreecentigrade for about 1.5 to 15 minutes.

When heating is completed, the presence or absence of the perfume of thefragrance material in the conductive paste (or at least partly hardenedproduct) is determined by an inspection. Such inspection may beperformed by an operator who have a normal olfactory perception or usinginspection machine. When the perfume of the conductive paste issubstantially absent, the fragrance ingredient is sealed within thehardened product due to hardening of the conductive paste, so thatcompletion of the hardening operation may be confirmed.

When the perfume of the conductive paste remains (containing the casewhere the perfume still remains although the level of the perfume isreduced compared with before heating), the fragrance ingredient is notsufficiently sealed within the hardened product. Thus, it is consideredthat the hardening operation is not sufficient, so that completion ofthe hardening can not be confirmed. Accordingly, in this case, hardeningoperation and the following inspection should be repeated until thehardening can be confirmed by confirming the absence of the perfume.

In this way, completion of the hardening of the resin in the conductivepaste can be confirmed based on the presence or absence of the perfumeof the conductive paste.

When completion of the hardening of the resin is confirmed, theconductive paste becomes to be a conductive hardened product. Theelectric components are mechanically and electronically bonded to thewiring circuit board, thereby mounted.

The electric-component mounted body obtained as mentioned above may beinstalled in a various electric/electronic components. Theelectric/electronic components produced by the present embodiment are,for example portable electronic devices such as mobile phone andheadphone stereos, the devices used for processing or preservation offoods, for example, rice cooking device, microwave oven, refrigerator,and the devices used for health and beauty, for example, body fat scale,skin moisture measuring system, electric toothbrush and electric shaver.

According to the method of preparing electric/electronic components inthe present embodiment, completion of the hardening of the resin in theconductive paste can be confirmed based on the perfume of the conductivepaste, so that an inspection at a low cost with a high degree ofaccuracy can be performed. The electric-component mounted body obtainedby the preparing method in the present embodiment, therefore theobtained electric/electronic components attains a high reliability ofquality.

EXAMPLE

Hereinafter, the bonding material for mounting electric devices of anyof the first to third inventions of the present application, the circuitboards having such the bonding material and the electric/electroniccomponents being equipped with such circuit boards are illustrated inmore detail through Inventive Examples and Comparative Examples.

(First Invention) 1. The Bonding Material for Mounting Electric Devices

First, an epoxy resin ingredient, a latent hardening agent ingredient,an inorganic thickening materials, conductive particles and reformingagent A as shown below are blended and kneaded in a roll mixer anddefoamed by subjecting the blend to a depressurization operation (lowerthan or equal to 10 mmHg) to obtain a bonding material for mountingelectric devices as an inventive example of the first invention(Examples 1-3). The blend ratio of each ingredient is shown in Table 1.

Epoxy resin: 1,6-hexanedioldiglycidyl ether type epoxy resin (availablefrom Asahi Denka Kogyo Co. Ltd, Trade name: ACR epoxy);

Latent hardening agent: 2-methylimidazoleazine (Japan Epoxy Resin Co.Ltd., trade name: epicure M12AZ);

Inorganic thickening material: AEROSIL (Registered Trademark) #200(manufactured by Nippon Aerosil Co., Ltd.)

Conductive particles: Silver powder having a mean diameter of about 6micrometer (manufactured by Mitsui Mining & Smelting Co., Ltd.)

Reforming agent A: trimethylolpropane tristhiopropionate (liquid) whichis a sulfur-containing compound.

As Comparative Examples, the same experiments with the ingredients andthe conditions as in the above Examples except that the kinds and theblending amount of the reforming agents were changed as shown in Table 1(Comparative Examples 1-5).

Reforming agent B: silane coupling agent; vinyltrimethoxysilane(manufactured by Dow Corning Toray Co., Ltd.)

Reforming agent C: Titanate-type coupling agent; Plainact KR TTS(manufactured by Ajinomoto Fine-Techno. Co., Ltd.)

TABLE 1 Compositions of the bonding materials (parts by weight) latentinorganic con- reforming epoxy hardening thickening ductive agent resinagent agent particles A B C Example 1 100 15 1 500 40 — — Example 2 10015 1 500 1 — — Example 3 100 15 1 500 100 — — Comparative 100 15 1 500 —— — Example 1 Comparative 100 15 1 500 — 3 — Example 2 Comparative 10015 1 500 — — 3 Example 3 Comparative 100 15 1 500 0.5 — — Example 4Comparative 100 15 1 500 110 — — Example 5

In order to evaluate the properties of the bonding materials obtained inExamples 1-3 and Comparative Examples 1-5, the hardening temperaturesand Preservation period (days) are obtained as follows:

1) Hardening Temperature

Eight samples of unhardened bonding materials and eight glass-epoxyboards were provided. Each bonding material was directly printed on asurface of each glass-epoxy board, respectively, which surface wasalready coated with a copper plating. Each of the printed bondingmaterial had a rectangular parallelepiped form having 1 mm length, 1 mmwidth and 0.1 mm height. Each of samples was heated for 10 minutes at 60degree centigrade, 70 degree centigrade, 80 degree centigrade, 90 degreecentigrade, 100 degree centigrade, 110 degree centigrade, 120 degreecentigrade and 130 degree centigrade, respectively, followed by beingnaturally-cooled to a room temperature (about 25 degree centigrade).Alternatively, a transfer printing technique which provides the accuracycomparable with the above printing could be adopted instead of theprinting method. Each of the obtained samples was settled in aDifferential Thermal Analyzer (DTA) and heated at a uniform rate ofheating (10 degree centigrade per minutes), thereby heat quantity Q1which was used during the period from just after starting of heating atthe predetermined temperature until the completely hardened state wasmeasured, respectively.

Separately, one sample of unhardened bonding material was settled in theDifferential Thermal Analyzer (DTA) and heated at a uniform rate ofheating (10 degree centigrade per minutes), thereby heat quantity Q0which was used during the period from the unhardened state until thecompletely hardened state was beforehand measured. Then, each hardeningrate R (%) by heating at each of the predetermined temperature asmentioned in the above was calculated on each sample according to theformula (I):

$\begin{matrix}\left\lbrack {{formula}\mspace{14mu} 1} \right\rbrack & \; \\{R = {\frac{Q_{0} - Q_{1}}{Q_{0}} \times 100(\%)}} & (1)\end{matrix}$

Among the temperature conditions which provide 90% or more of hardeningrate (R), the lowest temperature was established as the hardeningtemperature. According to the inventor's extensive experience, it isknown that a bonding material indicates an excellent reliabilityrelating to mechanical and electrical bonding for a long period as faras it shows a hardening temperature or 90% or more.

2) Period of Stable Preservation

Just after the sample of the bonding material was prepared, theviscosity η0 thereof was measured. Thereafter, the viscosity η1 of thesame sample was repeatedly measured while keeping the temperature of thesample at about 25 degree centigrade. An E type Viscometer was used tomeasure the viscosity. The period of days that the measured viscositytook to reach a condition showing η1≦2×η0 was assigned as the “Period ofstable preservation.” According to the inventor's extensive experience,it is known that a bonding material which shows 7 days or more of Periodof stable preservation involves no practical problem.

The results of the above evaluation of the properties are set forth inthe following Table 2:

TABLE 2 Evaluation of properties of the bonding materials hardeningPeriod of stable temperature preservation (° C.) (days) Example 1 70 20Example 2 80 28 Example 3 70 8 Comparative 120 24 Example 1 Comparative120 23 Example 2 Comparative 130 22 Example 3 Comparative 120 24 Example4 Comparative 60 2 Example 5

As understood from Table 2, each bonding material in Examples 1-3 showstoo low hardening temperature, and also practically suitable Period ofstable preservation. On the other hand, each bonding material inComparative Examples 1-4 shows higher hardening temperature rather thanthat of the bonding materials of Examples 1-3 and the bonding materialin Comparative Example 5 did not show sufficient preservation stability.

2. Preparation of Circuit Board and Performance of Electric/ElectronicDevice Installing the Circuit Board Therein

Using each of the bonding materials obtained from the above Examples 1-3and Comparative Examples 1-3, a circuit board was prepared and theperformance of the electric/electronic device equipped with the abovecircuit board was measured, respectively.

In order to grasp the maximum temperature of a board when the board isheated in a reflow oven, a board to which a temperature sensor beingattached was passed through the reflow oven at each conditionscorresponding to each of the hardening temperatures (Table 1) of thebonding materials of Examples 1-3 and Comparative Examples 1-3 for 10minutes of heating period, thereby the temperature that the board wassubjected to was measured over time. Each temperature profile of themaximum temperature obtained in the above measurement are shown in Table3 as reflow peak temperature of each Example.

Then, using each bonding material of Examples 1-3 and ComparativeExamples 1-3, the bonding material was applied to the surface of theelectrode on a board by printing or transfer printing and then anelectric component was arranged onto the circuit board so that theelectrodes of the electric component were suitably aligned with andcontacted with the bonding material on the board.

Thereafter, each board was passed through a reflow oven which is set ateach conditions corresponding to each of the hardening temperatures ofthe bonding materials of Examples 1-3 and Comparative Examples 1-3 for10 minutes of heating period, thereby each of the electric componentswere mounted on the board to obtain a mounted circuit board,respectively. As the electric component, a connector (a molded componentmade of polyethylene) having an allowable temperature of 90 degreecentigrade was used.

Using each circuit board, a compact disc player as theelectric/electronic device was assembled, respectively. The aboveobtained electric/electronic device was tested whether or not itperforms properly. The results of the above test are shown in Table 3.

TABLE 3 Heating conditions in the production of the circuit board andthe performance of the obtained electric/electronic device Reflow PeakTemperature performance of (° C.) electric device Example 1 75 normallyoperated Example 2 86 normally operated Example 3 70 normally operatedComparative 129 not operated Example 1 Comparative 131 not operatedExample 2 Comparative 135 not operated Example 3

As understood from Table 3, each electric device equipped with a circuitboard prepared using the bonding material in Examples 1-3 showed areflow peak temperature lower than the allowable temperature of theelectric device and could normally operate without causing thermaldamage of the electric device. On the other hand, each electric deviceequipped with a circuit board prepared using the bonding material inComparative Examples 1-3 showed a reflow peak temperature higher thanthe allowable temperature of the electric device and could not operateproperly, which seemed to be due to causing thermal damage of theelectric device.

(Second Invention) Example 4

To 100 parts by weight of ethanol, 100 parts by weight of silver oxidesand 1 parts by weight of 1,10-decanedithiol were added, to whichultrasonic wave (22.9 kHz, 100 W) was subjected for two hours to obtainsilver nano-particles (having a mean diameter of about 8 nm) from silveroxides. Thus, a dispersion of the silver particles (also referred to as“silver nano-particles” in this example) was prepared. To the obtaineddispersion, 100 parts by weight of another silver particles (having amean diameter of about 5 μm) and 20 parts by weight of bisphenol F typeepoxy resin (trade name “Epikote 871”, manufactured by Japan Epoxy ResinCo. Ltd.) based on 100 parts by weight of the silver particles in thedispersion were mixed and the mixture was kneaded by a three-roll mixerto obtain a conductive paste.

Example 5

To 100 parts by weight of ethanol, 100 parts by weight of silverparticles (having a mean diameter of about 10 μm) and 1 parts by weightof 1,10-decanedithiol were added to obtain a dispersion of silverparticles. To the obtained dispersion, 100 parts by weight of anothersilver particles (having a mean diameter of about 5 μm) and 20 parts byweight of bisphenol F type epoxy resin (trade name “Epikote 871”,manufactured by Japan Epoxy Resin Co. Ltd.) based on 100 parts by weightof the silver particles in the dispersion were mixed and the mixture waskneaded by a three-roll mixer to obtain a conductive paste.

Example 6

The procedure of Example 4 was repeated to obtain a conductive materialexcept that 1,10-decanedithiol as the sulfur-containing compound havingan end group of thiol group was replaced with 1,10-diaminodecane as thesulfur-containing compound having an end group of amino group.

Comparative Example 6

To 100 parts by weight of ethanol, 100 parts by weight of nickelparticles (having a mean diameter of about 5 μm) and 1 parts by weightof 1,10-decanedithiol were added to obtain a dispersion of nickelparticles. To the obtained dispersion, 10 parts by weight of bisphenol Ftype epoxy resin (trade name “Epikote 871”, manufactured by Japan EpoxyResin Co. Ltd.) based on 100 parts by weight of the nickel particles inthe dispersion were mixed and the mixture was kneaded by a three-rollmixer to obtain a conductive paste.

In order to evaluate the properties of the conductive materials obtainedin Examples 4-6 and Comparative Examples 6, the preservation stabilityand the specific resistance were measured according to the followingmethods.

Preservation Stability (or life): A conductive paste is preserved in aconstant-temperature bath under an air atmosphere which is set to keep25 degree centigrade and the period of time until the conductive pastelooses flowability, in particular until the viscosity of the conductivepaste exceeds about 50 Pa-s was measured for a month.

Specific Resistance: A conductive paste was coated on the surface of aPET (polyethylene terephthalate) film at a region of 3 mm width and 150mm length with 50 μm thickness, which film was irradiated with aultraviolet ray at an accumulated amount of light of 5000 mJ, followedby being heated at a predetermined temperature for 30 hours to obtain ahardened product. The volume resistivity of thus obtained hardenedproduct was measured according to JIS (Japanese Institute Standard)K6911, and from the result the specific resistance was calculated. Theresults are shown in table 4.

TABLE 4 Comparative Example 4 Example 5 Example 6 Example 6 Preservationover over over 2 hours Stability 1 month 1 month 1 month Specific 1 ×10⁻⁵ 2 × 10⁻⁴ 1 × 10⁻⁵ 5 × 10⁻³ Resistance (Ω) (120° C.) (120° C.) (200°C.) (120° C.) (heating temperature)

The conductive paste of Examples 4-6 did not lose flowability within theperiod of the of the preservation reliability test (one month) andmaintained a high level preservation reliability (Table 4). The reasonseems to be that the sulfur-containing compound coordinates at the thiolend group or the amino end group thereof with the surface of the silverparticles to form a metal coordination compound, thereby the thiol groupor the amino group being capped, so that they did not react with theepoxy resin to cause the hardening reaction.

In the conductive paste of Examples 4-6, after the preservation testfinished, it was visually confirmed that the silver particles werestably dispersed and the agglomeration of the silver particles was notobserved. In particular, although the conductive paste of Example 4contained nano-sized particles which tend to easily agglomerate, itseems that such particles could stably exist in the resin by forming ametal coordination compound.

Further, the conductive paste of Examples 4-6 showed sufficientlysatisfactory low resistance as the conductive material in the specificresistance test (Table 4). The reason seems to be that thesulfur-containing compounds having the thiol group or the amino groupdissociated from the silver particles by irradiation of ultraviolet rayand the following heating, the dissociated sulfur-containing compoundperformed as the hardening agent to harden the resin, so that silverparticles came to contact one another or got closer to each other afterthe resin volumetrically shrinked and hardened.

In particular, the conductive paste of Example 4 showed a much lowerresistance rather than the conductive paste of Example 5. The reasonseems to be that the silver nano-particles sintered at a low temperatureby the heating in the specific resistance test.

Meanwhile, apart from the conductive paste of Examples 4 and 5, thespecific resistance of the conductive paste of Example 6 could not bemeasured at the heating temperature of 120 degree centigrade and showedno conductivity. The reason seems to be that the sulfur-containingcompound having the amino end group did not dissociate from the silverparticle and could not perform as the hardening group for the epoxyresin. When the heating temperature was increased to 200 degreecentigrade as shown in Table 4, it was confirmed that the conductivepaste showed a sufficiently low resistance.

On the other hand, as to the conductive paste of Comparative Example 4,the specific resistance thereof could be measured at the heatingtemperature of about 120 degree centigrade. Such resistance value wasallowable level for the conductive material. The reason seems to be thatthe sulfur-containing compounds could perform as the hardening agent forthe epoxy resin by the irradiation of ultraviolet ray and the heating toharden the resin, so that nickel particles came to contact one anotheror got closer to each other after the resin volumetrically shrinked andhardened.

However, the period of stable preservation of the conductive paste ofComparative Example 4 was too short and was merely two hours. The reasonseems to be that the thiol end group of sulfur-containing compoundexisted freely without being coordinated with the surface of the nickelparticles, so that the sulfur-containing compound reacted with the epoxyresin to cause the hardening the resin.

(Third Invention)

As the inventive examples and the Comparative Examples of the conductivepaste of the present third invention, various kinds of conductive pastewere prepared by mixing the constituents shown in Table 5 with the ratioshown in Table 6. In these inventive examples and the ComparativeExamples, common materials are used as the resin and the conductivefillers. Bisphenol A type epoxy resin was used as the resin, and silverparticles having a mean diameter from 2-15 μm (Trade Name “silcoat”,manufactured by Fukuda Metal Foil & Powder Co., Ltd) was used as theconductive particles. As the hardening agent, an imidazole type hardener(Trade Name “Curezole (registered trademark)”, Shikoku Chemicals, Co.Ltd.) or a polymercaptan type hardener (mercaptopropionic acid) wasused. In the inventive example, limonen or ethylvanillin was used as thefragrance, on the other hand, in the Comparative Example, no fragrancewas used.

TABLE 5 Constituent hardening conductive number resin agent fillerfragrance Example 7 bisphenol imidazole type silver limonen A typehardener particle epoxy resin Example 8 bisphenol polymercaptan silverethyl- A type type hardener particle vanillin epoxy resin Example 9bisphenol polymercaptan silver cinnamic A type type hardener particleacid epoxy resin Comparative bisphenol imidazole type silver — Example 7A type hardener particle epoxy resin Comparative bisphenol polymercaptansilver — Example 8 A type type hardener particle epoxy resin

TABLE 6 constituent hardening conductive number resin agent fillerfragrance Example 7-9 100 15 500 10 Comparative 100 15 500 0 Example 7-9

Relating to each of Examples 7 and 8 as well as Comparative Examples 7and 8, a test whether a human having normal olfactory sense could feelunpleasant stench when he brings his nose to the conductive paste by onehundred people of experimental subjects. Herein, an index of feelingunpleasant stench is defined by the formula:

$\begin{matrix}\left\lbrack {{formula}\mspace{14mu} 2} \right\rbrack & \; \\{\left( {{index}\mspace{14mu} {of}\mspace{14mu} {feeling}\mspace{14mu} {unpleasant}\mspace{14mu} {stench}} \right) = \frac{\begin{pmatrix}{{number}\mspace{14mu} {of}\mspace{14mu} {experimental}} \\{{subjects}\mspace{14mu} {who}\mspace{14mu} {felt}\mspace{14mu} {unpleasant}}\end{pmatrix}}{\left( {{sum}\mspace{14mu} {of}\mspace{14mu} {experimental}\mspace{14mu} {subjects}} \right)}} & (2)\end{matrix}$

The results are shown in Table 7.

TABLE 7 index of feeling number unpleasant stench (-) Example 7 0.2Comparative 0.2 Example 7 Example 8 0.4 Comparative 0.9 Example 8

In each Comparative Examples 7 and 8, the same procedure was repeated asthe inventive Examples 7 and 8, respectively, except that the fragrancewas not added thereto. With reference to Table 7, when inventive Example7 is compared with Comparative Example 7, the index of feelingunpleasant stench was lower in inventive Example 7 rather thanComparative Example 7, and also the index of feeling unpleasant stenchwas lower in inventive Example 8 rather than Comparative Example 8.Accordingly, it was confirmed that inventive Examples can substantiallyreduce the unpleasant stench rather than Comparative Examples which donot use fragrances.

Volume resistivity of the hardened product obtained from each of Example9 and Comparative Example 8 was measured. The conductive paste of eachExample was hardened by heating at a temperature of 100 degreecentigrade for 10 minutes and then the Volume resistivity of each samplewas measured according to Japanese Industrial Standard (JIS) K 6911. Forreference, the Volume resistivity of Comparative Example 7 was measured.The results are shown in Table 8.

TABLE 8 Volume resistivity number (Ω cm) Example 9 3 × 10⁻⁴ Comparative5 × 10⁻³ Example 8 Comparative 2 × 10⁻⁴ Example 8

In Comparative Example 8, the same procedure was repeated as theinventive Example 9 except that the fragrance was not added. Withreference to Table 8, the volume resistivity of inventive Example 9 wascompared with that of Comparative Example 8. The volume resistivity ofinventive Example 9 was lower than that of Comparative Example 8, sothat it was confirmed that inventive Example 9 showed suitableconductivity. In Example 9, cinnamic acid was used as the fragrance,which has a reducing ability. Thus, it was conceived that sulfurizationof the silver particles, which were used as the conductive filler, wasefficiently prevented by cinnamic acid although a compound having thiolgroup (—SH) was used as the hardening agent in Example 9.

Also with reference to Table 8, in case where a fragrance is not used,Comparative Example 8 which uses a compound having a thiol group as ahardening agent showed higher volume resistivity rather than ComparativeExample 7 which uses a compound without a thiol group as a hardeningagent. It was conceived that a thiol group sulfurized the metal in theconductive filler to form a sulfide when the conductive paste did notcontain a compound having a reducing ability.

An easiness of inspecting completion of the hardening in the method ofproducing electric components mounted products by mounting electriccomponents on circuit boards with the hardened product obtained from theconductive pastes was measured in Example 8 and Comparative Example 8.In Example 8, the hardening of the conductive paste did not completedwhile the perfume of the conductive paste is present. Thus, it can beconceived that an operator can determine that the hardening of theconductive paste was completed when the perfume of the conductive pastecomes to absent, so that evaluated with an open circle (∘). To thecontrary, the method to determine completion of the hardening is limitedin the Comparative Example 8. Such method is either to inspect visuallythe change of the color tone of the resin, or to measure the connectionstrength or connection resistance. It is difficult to determine thecolor tone due to the influence of the color of the conductive filler inthe former case, and any measuring apparatus is necessary in the lattercase. Accordingly, Comparative Example 8 was difficult as to inspectingcompletion of the hardening rather than Example 8, so that evaluatedwith a triangle (Δ).

Then, an applicability ratio of the conductive paste among electricdevices was measured. Here, the applicability ratio of the conductivepaste among electric devices is defined by the formula (3):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack & \; \\{\left( {{applicability}\mspace{14mu} {ratio}} \right) = {\frac{\begin{pmatrix}{{number}\mspace{14mu} {of}\mspace{14mu} {allowable}} \\{{electric}\mspace{14mu} {device}}\end{pmatrix}}{\left( {{sum}\mspace{14mu} {of}\mspace{14mu} {electric}\mspace{14mu} {device}} \right)} \times 100}} & (3)\end{matrix}$

Note that the denominator “sum of electric device” means and thenumerator “number of allowable electric device” in the above Formula 3are made on the basis of inventor's broad vision. The results are shownin table 9.

TABLE 9 easiness of applicability ratio number inspection (%) Example 8◯ 60 Comparative Δ 20 Example 8

As shown in Table 9, inspection was easier in Example 8 rather than inComparative Example 8 and the applicability ratio of the conductivepaste among electric devices in Example 8 was significantly improvedrather than in Comparative Example 8.

INDUSTRIAL APPLICABILITY

The circuit boards prepared using any conductive paste of first to thirdinvention of the present application can be used for any of arbitraryelectric/electronic devices. The examples of such electric/electronicdevices are as shown below:

Portable electronic devices such as video-camera, portable CD, portableMD, portable DVD, mobile phone and laptop computer;

Typically stationary settled electronic devices such as stereo set,desk-top type computer, video telephone, DVD player, CD player, DVDrecorder, CD recorder and television set;

Home appliance electronic devices such as rice cooking device, microwaveoven, refrigerator, cleaner, washing machine, air conditioner, lightingapparatus, intercom, security camera, monitoring camera, gas leakagedetector and the toilet seat with the washing functions;

Electronic devices for vehicles, for example for automobile andtwo-wheeled motor vehicle, such as car stereo, car navigation system,car air-conditioner, car sensor, engine controller, loading camera,automatic brake safe control system (ABS) and headlight.

The conductive bonding materials in the first and second inventions areapplicable to various fields such as for forming a circuit wiringpattern on a circuit board; the materials for forming electricconnections among multilayer circuit boards; and the bonding materialsfor bonding materials for forming mounted electric components in thetechnical field of forming electric/electronic circuit

The conductive bonding materials in the third invention is applicable tovarious fields such as portable electronic devices, devices forprocessing or preservation of foods, and home appliance electronicdevices as the electric-component mounted bodies.

1-10. (canceled)
 11. A conductive bonding material comprising aconductive particle ingredient, an epoxy resin ingredient, and ahardening agent ingredient for said epoxy resin characterized in thatsaid epoxy resin ingredient has a linear or cyclic sulfur-containingcompound.
 12. The conductive bonding material according to claim 11,characterized in that the material further contains a thickening agent.13. The conductive bonding material according to claim 11, characterizedin that the conductive particle ingredient is metallic particles, thesulfur-containing compound coordinates with the surface of the metallicparticles, and the thiol containing compound dissociates from thesurface of the metallic particles to form an epoxy hardening agentingredient upon being subjected with a predetermined condition.
 14. Theconductive bonding material according to claim 13, characterized in thatthe metallic particles are selected from the group of gold, silver andcopper particles.
 15. The conductive bonding material according to claim13, characterized in that the operation to be subjected to apredetermined condition is selected from the conditions comprising beingirradiated with ultraviolet ray or electron ray, or being heated. 16.The conductive bonding material according to claim 11, characterized inthat the metallic particles have a mean diameter in a range from 1 nm to100 μm.
 17. The conductive bonding material according to claim 11,characterized in that the material further contains a fragrancematerial.
 18. The conductive bonding material according to claim 17,characterized in that the conductive particles ingredient is metallicparticle and that the fragrance material is a material having a reducingability.
 19. A method of preparing an electric/electronic circuit boardcomprising; applying a conductive bonding material according to claim 11to a surface of a board; followed by activating an epoxy resin hardeningagent.
 20. An electric/electronic device having one or more circuitboards that were prepared through the method according to claim 19.